1. Field of the Invention
The present invention relates to an image display delay time shortening apparatus during channel change, a method thereof and a broadcasting receiving apparatus thereof, and more particularly to an image display delay time shortening apparatus during channel change, a method thereof and a broadcasting receiving apparatus thereof by which a sequence header is detected from a received video stream and stored in a relevant region of a channel information table in a memory, and a sequence header corresponding to a channel changed when the channel is to be changed is extracted from the relevant region of the channel information table to establish an initial value of a decoder, thereby enabling to shorten a time in which an image starts to be displayed.
2. Description of the Related Art
In an analogue television (TV) receiver conforming to NTSC (National Television Standard Committee) protocol, a channel change is implemented in such a manner that a tuning frequency is changed by a channel change signal and a broadcasting signal corresponding to the tuning frequency is received.
In the NTSC signal, horizontal and vertical synchronous information are respectively received in the interval of 63 μs and 33 ms, and the analogue TV receiver uses the information for channel change to rapidly display the received broadcasting signal on a screen.
However, when a digital TV receiver displays on a screen a digital broadcasting signal by receiving the digital broadcasting signal according to ATSC (Advanced Television Standards Committee) protocol, much more time is consumed compared with displaying of an image on a screen by receiving the analogue broadcasting signal because a moving picture data encoded by MPEG (Moving Picture Experts Group) protocol should be decoded.
To be more specific, moving picture data of a digital broadcasting signal differs in terms of resolutions, aspect ratios of pixels, and display period of images. As a result, a digital broadcasting signal contains a sequence header including information on resolutions and aspect ratios of pixels. A digital TV receiver extracts a sequence header from a received digital broadcasting signal and establishes an initial value of a video decoder according to the extracted sequence header. The video decoder decodes a video stream in response to the initial value.
The sequence header is stored in an elementary stream packet and transferred. Therefore, the digital TV receiver uses a Program Specific Information (PSI) included in the received digital broadcasting signal to extract a Program Identifier (PI), and seeks the elementary stream packet from the extracted PI to extract a sequence header.
The sequence header is recommended to be inserted into a digital image signal per 0.5 second and transmitted in the ATSC digital television standard document A/54, but it is just a recommendation. Accordingly, there is a difference in an insertion time of the sequence header according to broadcasting stations or broadcasting contents producers, and practically, broadcasting stations or broadcasting contents producers insert a sequence header into a digital image signal at a time interval longer than the recommended time of 0.5 second.
When a channel of a digital TV receiver is changed, a video decoder immediately implements a decoding operation to thereby enable to display an image within an instant time if a sequence header is included in a digital broadcasting signal received at the start of the channel change.
However, if the sequence header is not contained in the digital broadcasting signal received at the start of channel change, an initial value of the video decoder cannot be established resulting in non-implementation of the decoding operation. Consequently, the video decoder waits until the sequence header is received, and starts to display the image on a screen once the sequence header is received.
If the channel is changed, the video decoder is reset to delete initial values of the decoder erstwhile established. As a result, if the sequence header is not contained in the video stream received at the start of the channel change, the decoder cannot establish an initial value and implement the decoding, such that the decoder should wait until the sequence header is received.
An image display delay time reportedly occurs for 1˜2 seconds on the average. If a channel is changed, viewers can view images once the image display delay time passes.